Physically inactive adults are prevalent worldwide. This study compared the effects of short-term high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) on heart rate variability (HRV) in physically inactive adults as a preliminary study. Thirteen physically inactive male adults (27.5 ± 3.80 years) were randomly assigned to HIIT (N = 7) or MICT (N = 6). The HIIT program consisted of 20 min of interval training with cycling to rest ratio of 10/50 s at ≥90% HR_peak, while the MICT program consisted of 40 min of continuous cycling at 60–75% HR_peak. Both groups completed eight sessions of training within two weeks. Time and frequency domains of HRV were measured for 20 min with Actiwave-Cardio monitor (CamNtech, UK). The number of R-R interval and inter-beat interval (IBI) were significantly improved (p < 0.05) in both HIIT and MICT programs following eight sessions of training. A significant interaction effect for group by time was found in the lnLF/HF ratio (p < 0.05) where it was only improved in the HIIT group from pre- to post-test. The HIIT program is superior to MICT in improving HRV in physically inactive adults. The HIIT program can be applied as a time-efficient program for improving cardiac-autoregulation.

Purpose: To evaluate if sedentary time (ST) is associated with heart rate (HR) and variability (HRV) in adults. Methods: We systematically searched PubMed and Google Scholar through June 2020. Inclusion criteria were observational design, humans, adults, English language, ST as the exposure, resting HR/HRV as the outcome, and (meta-analysis only) availability of the quantitative association with variability. After qualitative synthesis, meta-analysis used inverse variance heterogeneity models to estimate pooled associations. Results: Thirteen and eight articles met the criteria for the systematic review and meta-analysis, respectively. All studies were cross-sectional and few used gold standard ST or HRV assessment methodology. The qualitative synthesis suggested no associations between ST and HR/HRV. The meta-analysis found a significant association between ST and HR (β = 0.24 bpm per hour ST; CI: 0.10, 0.37) that was stronger in males (β = 0.36 bpm per hour ST; CI: 0.19, 0.53). Pooled associations between ST and HRV indices were non-significant (p > 0.05). Substantial heterogeneity was detected. Conclusions: The limited available evidence suggests an unfavorable but not clinically meaningful association between ST and HR, but no association with HRV. Future longitudinal studies assessing ST with thigh-based monitoring and HRV with electrocardiogram are needed.

We evaluated the effects of a simulated workday of prolonged sitting on blood pressure (BP) and pulse wave velocity (PWV) and examined whether posture (seated vs. supine) affected responses. Participants (n = 25) were adults, with overweight/obesity and elevated BP, and performed seated desk work for 7.5 h. BP and PWV were measured in seated and supine postures at baseline (7:15 a.m.), midday (12:05 p.m.), and afternoon (4:45 p.m.). Generalized linear mixed models evaluated the effects of prolonged sitting on BP and PWV within each posture and interactions by posture and sex. In the recommended postures, seated BP and supine carotid-femoral pulse wave velocity (cfPWV) and carotid-ankle pulse wave velocity (caPWV), but not carotid-radial pulse wave velocity (crPWV), significantly increased over the simulated seated workday (all p < 0.05; effect sizes [d] ranged from 0.25 to 0.44). Whilst no posture-by-time interactions were observed (p > 0.05), BP, caPWV, and crPWV were higher when seated versus supine (main effects of posture p < 0.05; d ranged from 0.30 to 1.04). Exploratory analysis revealed that females had greater seated BP responses (p for interaction 0.05). A simulated workday of prolonged sitting increased seated BP and supine cfPWV and caPWV, and posture minimally influenced these responses. These results add to the evidence suggesting a deleterious effect of prolonged sitting on cardiovascular health.

Objectives: We assessed sedentary behavior (SB) patterns and examined its associations, by domain, with cardiovascular disease (CVD) risk measures in desk workers (N = 273). Methods: Sedentary behavior was measured by activPAL3 and partitioned into occupational and nonoccupational SB. Cardiovascular disease risk measures included blood pressure, pulse wave velocity, heart rate, and heart rate variability. Paired t tests evaluated patterns of SB across domains. Linear regressions estimated associations of occupational and nonoccupational SB with CVD risk measures. Results: Participants spent 69% of their time in SB; higher proportions were accumulated during occupational versus nonoccupational time. Higher all-domain SB was only associated with higher pulse wave velocity. Paradoxically, greater nonoccupational SB unfavorably associated with CVD risk measures, while higher occupational SB favorably correlated to CVD risk measures. Conclusions: Observed paradoxical associations suggest that domain should be considered in efforts to improve cardiovascular health by reducing SB.

Background: Low moderate-to-vigorous-intensity physical activity (MVPA) and high sedentary time (ST) may contribute to cardiovascular disease (CVD) risk in women, perhaps via cardiac autonomic dysregulation. We examined associations of total, leisure, and occupational MVPA and ST with cardiac autonomic regulation in women. Methods: Data were from 522 women (age = 37.7 ± 5.7 years; 59%white) who participated in the follow-up study of the Pregnancy Outcomes and Community Health Study (between 2011 and 2014). MVPA and ST (hours/day) were self-reported using the Modifiable Activity Questionnaire. Cardiac autonomic regulation was assessed by calculating heart rate variability (HRV) indices (resting heart rate, natural logarithm standard deviation of normal R-R intervals; lnSDNN [total variability], natural logarithm root mean square of the successive differences; lnRMSSD [cardiac parasympathetic activity]) with Kubios software from a 5-minute, seated electrocardiogram. Progressive generalized linear models evaluated associations of total, leisure, and occupational MVPA and ST with HRV indices while adjusting for confounders (demographics, health-related factors), and then potential mediators (clinical variables). A final model evaluated the relationship between ST and HRV stratified by MVPA level. Results: Adjusting for confounders, total and leisure MVPA were associated with favorable lnSDNN ( B = 0.027 [ p = 0.014] and B = 0.074 [ p = 0.009], respectively) and lnRMSSD ( B = 0.036 [ p = 0.015] and B = 0.075 [ p = 0.043], respectively). Adjustment for mediators tended to strengthen the observed significant associations. No associations were found between occupational MVPA or any ST measure with HRV indices ( p > 0.05). Neither MVPA nor ST were associated with heart rate. When stratified by MVPA level, leisure ST was associated with unfavorable lnRMSSD ( B = −0.041, [ p = 0.042]) only among women who did not meet leisure MVPA recommendations. Conclusion: Cardiac autonomic dysregulation may be a mechanism through which low leisure MVPA and, among low-active women, high leisure ST contribute to CVD risk among women.

Background: Arterial stiffness, measured by pulse wave velocity (PWV), is a purported mechanism linking sedentary behavior to cardiovascular disease. This secondary analysis compared associations between measured carotid–femoral PWV (cfPWV) and carotid–radial (crPWV) responses to an acute bout of prolonged sitting with mathematically estimated cfPWV (ePWV). Methods: Overweight/obese adults with elevated blood pressure were enrolled (n = 25; 42 ± 12 yrs; 64% males). Participants performed an 8 h simulated workday of mostly sitting. cfPWV and crPWV were measured while supine in the morning, midday, and afternoon. ePWV was calculated at the same timepoints using age and seated mean arterial pressure (MAP). Pearson correlation coefficients associated ePWV with cfPWV and crPWV. Generalized linear models separately examined the effects of time on cfPWV, crPWV, and ePWV. Results: ePWV significantly associated with cfPWV and crPWV (r = 0.69 and 0.55, respectively; p < 0.05) in the morning (baseline). cfPWV significantly increased over time (β = 0.52 ± 0.20 and 0.48 ± 0.21 with and without MAP adjustment, respectively; p < 0.05). In contrast, ePWV and crPWV did not significantly increase overtime (β = 0.14 ± 0.09 and 0.25 ± 0.23, respectively; p > 0.05). Conclusions: Our results suggest that, although ePWV is associated with cfPWV and crPWV at a fixed timepoint, ePWV responds differently to prolonged sitting and likely does not capture the same acute vascular responses.